Critical Thinking About Critically Ill Cats

Cats are very different from dogs when it comes to clinical signs of illness, response to treatment, and hospitalization. Cats hide their pain and often do not show signs of illness until they are very ill. Identifying and caring for critically ill cats therefore require veterinary nurses to recognize subtle signs and behaviors and to know which organ systems are most often involved in critical illness in this species.

Presentation and Triage

Because cats hide signs of pain and illness, triaging a scared, ill cat in the lobby through a carrier will not give an accurate picture of how it is doing. Sick cats should be assessed in an enclosed, quiet area. It is also important to get a brief but full history from the owner, including previous medical history, medications, and when the patient was last “normal.” Triage should be brief, and this process should only take approximately 5 minutes (BOX 1).

Assessment in the examination room should be performed quickly and include a complete physical examination (TABLE 1). The 5 vital assessments—temperature, pulse, respiration, pain, and nutrition—should be considered. Physical examination findings that should prompt concern for critical illness include hypothermia, bradycardia or tachycardia, pale mucous membranes, lateral recumbency, or pain.

Stabilization

Stabilizing critically ill cats requires the veterinary team to consider several issues that are unique to cats, such as their tendency to easily become volume overloaded and their different drug metabolism, blood volume, and blood types compared to dogs.

Stabilizing critically ill cats involves multiple steps; however, the less stress, the better for the patient. After physical examination, an intravenous catheter should be placed as long as the patient will tolerate it with minimal stress. If possible, draw blood for all necessary diagnostic tests when the catheter is placed to avoid multiple needle sticks for early blood samples. As long as the catheter is not preflushed, blood can be drawn through the catheter.

The gauge of the catheter is not important in unstable patients. Although studies have shown that larger catheters deliver fluids and drugs more quickly,¹ a successfully placed small-gauge catheter is better than struggling to get access with a larger gauge.

A jugular catheter or intraosseous catheter can also be considered if vascular access is problematic. In jugular access cases, if possible, ensure that blood samples to assess coagulation are drawn first.

An initial blood analysis should be run and auscultation of the heart should be performed. Blood pressure should also be measured. Specific stabilization measures will depend on patient presentation and clinician diagnosis.

Common Treatment Considerations

Shock

Shock is defined as poor tissue perfusion that leads to decreased cellular oxygen and subsequent inadequate cell energy. Ultimately, cellular death and organ failure can result. There are 4 types of shock, which can be the result of many kinds of critical illness, but all are characterized by decreased perfusion (BOX 2).

Shock in cats often presents as tachypnea, hypothermia, hypotension, and either bradycardia or tachycardia.² Cats in shock often arrive at the clinic in respiratory distress. They may also have depressed mentation or be laterally recumbent and have weak pulses and cool extremities as the body tries to perfuse the main organs (i.e., the kidneys, heart, brain).

The feline “shock organ” is the lungs.³ This means that the lungs are very susceptible to damage during shock events and will experience decreased perfusion. Stress from the underlying critical illness causes cytokines to be released, which in turn causes blood vessels to become dilated. Protein then “leaks” from blood vessels into the alveoli of the lungs, impairing their function and contributing to further decreased oxygen delivery to the rest of the body. It is therefore important to keep reassessing and listening to the lungs once stabilization is achieved.

It is also very important to keep critically ill feline patients calm and oxygenated. If possible, cats in shock should be placed in an oxygen cage instead of receiving flow-by oxygen, which can stress them more than help them. Veterinary nurses should also advocate for giving these patients pain medications or slight sedation to keep them calm in the stressful hospital environment.

Hypothermia can affect metabolism, platelet function, perfusion, and renal function, as well as increase cardiac arrest risk^2,3; therefore, hypothermia should be addressed with active warming (FIGURE 1).

Figure 1. A cat in the intensive care unit with a chest tube. This cat is receiving active warming.

The cat’s heart rate should also be monitored. In cats, it is difficult to assess an increase in heart rate if the patient is already under stress. In addition, if the heart rate drops below 160 beats per minute, intervention must occur as soon as possible.

Fluid Therapy

Fluid therapy should be undertaken carefully in critically ill cats for several reasons. One is that cats have a smaller total blood volume than dogs—around 60 mL/kg in cats compared with about 90 mL/kg in dogs. Another is that heart disease in cats can be silent until they have a critical illness or until after a fluid bolus is given. Therefore, special considerations should be implemented when giving a fluid bolus or blood products to a cat. Isotonic crystalloid boluses should be given in small increments and total 40 to 60 mL/kg. It is also important to watch the patient’s temperature, heart rate, and respiratory rate during a fluid bolus.⁴

Extra caution should be taken in any cat with suspected heart disease. Respiratory rate, heart rate, and temperature should be assessed and recorded frequently, potentially hourly. Cardiomyopathy is not uncommon in cats; therefore, veterinary nurses should listen for murmur sounds, although these can be difficult to discern as feline heart rates are often high. An electrocardiogram should be obtained to rule out any arrhythmias.

Fluids should not be given if the cat is suspected to be in heart failure, as a failing heart will be further compromised by additional intravenous fluid, leading to a further decrease in perfusion and worsening of shock as the fluid leaks into the lungs. In these cases, pulmonary edema can happen quickly and silently. Signs of fluid overload are crackles heard in the lungs, gallop-rhythm heart sounds, arrhythmias, weak pulses in the femoral arteries, and increased respiratory rate.

Transfusion Reactions

Cats have 3 blood types: A, B, and AB. Type A is the most common. If a critically ill cat requires a blood transfusion, it is very important to ascertain the cat’s blood type prior to the transfusion. Giving a type B cat type A blood will cause a severe and potentially fatal transfusion reaction.

It is important to monitor a feline blood transfusion very carefully. If any changes in temperature or mentation or dramatic changes in heart rate are noted, the transfusion must be stopped. Intravenous fluid therapy may be necessary to maintain blood pressure after a reaction. Before another transfusion is started, a crossmatch may be necessary.

Hyperglycemia

Hyperglycemia in critically ill cats can be caused by stress, which increases the release of catecholamines and lactate. Increased lactate is also an indication of decreased perfusion. Most of the time, stress-induced hyperglycemia does not need to be treated. However, if it is determined that hyperglycemia is due to a disease process like diabetic ketoacidosis, the underlying disease should be treated.

Hospitalization and Monitoring

Once a critically ill cat has been stabilized, it is important to keep stress and anxiety to a minimum to support healing and treatment (FIGURE 2). Cats should be hospitalized in a quiet, feline-only ward if possible. Pheromones can also be used to decrease stress.

Figure 2. A cat in the intensive care unit. The cat is being handled minimally and has owner belongings in the cage to increase comfort.

In cats, stress, anxiety, and pain can lead to aggression—often, in the author’s experience, the most aggressive patients in a hospital are cats. Understanding why the patient is aggressive will help with treatment. Is the cat in pain? Does it not like restraint? Has it never been in a kennel or hospital before? In some cases, chemical restraint may be indicated to allow for less stress for the patient and veterinary team. Critical thinking is very important in the nursing care of cats.

Liver Function

Blood analysis should be performed regularly to monitor liver function in critically ill cats. The liver controls many body functions, including metabolism and detoxification of substances and medications. Thiopurine methyltransferase is a liver enzyme that is important in metabolizing certain drugs. Cats are naturally deficient in this enzyme, which decreases their ability to metabolize these drugs and makes them more susceptible to toxicosis with these drugs at lower doses than dogs. Drug choices and dosages should be adjusted if liver or kidney disease is suspected due to metabolism of the drug.

Kidney Function

When a critically ill cat is hospitalized, it is important to monitor kidney function. Azotemia can be the result of congenital abnormalities, infection, dehydration, or toxins, although it is important to remember cats can hide clinical signs of kidney disease. Damaged kidneys also lack the ability to respond to decreases in vascular volume, leading to low blood pressure and further decreased perfusion through impairment of the renin-angiotensin-aldosterone system.⁵

A urinary catheter can be placed to monitor hydration status as well as kidney function via fluid intake and output (FIGURE 3).⁵ Urine output should be measured at least every 4 hours, and specific gravity can be measured to determine if the kidneys are concentrating the urine. If less than 2 mL/kg/h of urine is being produced, then kidney function should be questioned, and the patient is at risk of fluid overload and electrolyte abnormalities because the kidneys are not keeping up with fluid therapy.

Figure 3. A critically ill cat with multiple intravenous catheters, a urinary catheter, and a nasogastric tube.

Laboratory testing to evaluate kidney function includes measurement of creatinine and blood urea nitrogen. An SDMA (symmetric dimethylarginine) test, which evaluates a specific kidney biomarker, can also be used.

Pain

Veterinary nurses must assess pain in every patient. The best way to assess pain in a cat is during the physical examination, but signs of pain in cats can be very subtle (BOX 3). Increased blood pressure, heart rate, and temperature, as well as abnormal behavior, can all be signs of pain. Pain scoring systems, such as the Colorado State University Feline Acute Pain Scale and the Feline Grimace Scale, have been developed specifically for cats and can help make pain assessment more objective. Troubleshooting what will make the patient more comfortable can take a while, but it will help the patient in the long run.

Nutrition

Nutrition in critically ill cats is also very important; it is associated with shorter hospital stays as protein and energy support wound healing, immune function, intravascular fluid retention, and cell metabolism.⁶ Protein is especially important in cats, which have a high protein requirement. Cats that are critically ill benefit from early enteral nutrition (nasogastric or esophageal feeding tube).

Summary

Understanding feline physiology will help veterinary nurses better care for critically ill cats in the hospital setting. Knowing how disease conditions specifically affect cats helps improve treatment and gives these patients a better chance of going home healthy and in a timely manner.